(c) Size of Protected Area. The size and location of the protected area should be reviewed for adequate visibility, especially for approach and landing conditions. Crosswinds and runway light visibility during instrument landings need to be considered.
(d) Failure Analysis. A probable single failure of a transparency heating system should not adversely affect the integrity of the airplane cabin or create a potential danger of fire.
(4) Pitot-Static and Static Pressure Sources. If the air data system configuration of either the pitot or the static source(s) differs from that of the basic airplane, then airspeed and altimeter system calibrations should be evaluated for compliance with the certification requirements. A component surface temperature evaluation may be necessary to verify thermal analyses. Section 23.1325(b) requires that static pressure port design or location should be such that the correlation between air pressure in the static pressure system and true ambient atmospheric static pressure is not altered when the airplane encounters icing conditions.
Section 23.1325(b)(3) allows an anti-icing means or an alternate source of static pressure may be used in showing compliance with the requirement.
(5) Stall Warning and Angle-of-Attack Sensors. Ice could form on these sensors if these devices are not protected. When the icing approval requires installation of new or modified sensors, that sensor's function should be evaluated for compliance with the certification requirements. These sensors may not require heat for ice protection if substantiated by analyses.
A surface temperature evaluation may be necessary to verify thermal analyses. Consideration should be given to ice formations on the airframe in the vicinity of the sensor mounting location that may affect the sensor's operation.
(6) Pitot Tube. Section 23.1323 requires a heated pitot tube or an equivalent means of preventing malfunction due to icing. Section 23.1326 requires a pitot tube heat indicating system if a flight instrument pitot heating system is installed to meet ice protection requirements.
(7) Fluid (Freezing Point Depressant) Systems.
(a) Fluid Coverage. Dry air testing should include evaluation of fluid flow paths to determine that adequate and uniform fluid distribution over the protected surfaces is achieved.
Colored fluid or colored water with camera documentation may be used. A range of angles of attack should be evaluated with both high and low volume rates. Inlets or openings where fluid ingestion will have a detrimental effect should be evaluated.
(b) Aircraft Performance. Dry air testing should also include performance testing with the system operating since drag increases have been documented on previous certification programs.
(c) Temperatu re. The system should be functionally tested at the minimum part 25, Appendix C ambient temperatures.
(d) Windshield. The fluid anti-ice/deice systems may be used to protect propellers and windshields, as well as leading edges of airfoils. The fluid for windshield fluid systems, and for propeller fluid systems forward of the windshield, should be tested to demonstrate that it does not become opaque at low temperature.
(e) Cockpit Annunciations. Means of indicating fluid flow rates, quantity remaining, and so forth, should be evaluated to determine that the indicators are plainly visible to the pilot and that the indications provided can be effectively read.
(8) Compressor Bleed Air Systems. The effect of any bleed air extraction on engine and airplane performance should be examined and shown in the AFM performance data. The surface heat distribution analysis should be verified for varying flight conditions including climb, cruise, hold, and descent. A temperature evaluation may be necessary to verify the thermal analyses. If a minimum engine speed is required for ice protection system operation, the ability to descend should be evaluated. If compressor bleed air is used for anti-icing an engine cowl that is made of composite material, a thermal analysis/survey should be conducted to assure there is no engine cowl delamination or other structural failure.
(9) Ice Inspection Light(s). Ice inspection lights may be necessary if operations are dependent upon observing ice accumulations at night (§ 23.1419(d)). Ice inspection lights should be evaluated both in and out of clouds during night flight to determine that adequate illumination of the component of interest is available without excessive glare, reflections or other distractions to the flight crew. These tests may be conveniently accomplished both in and out of clouds during dry air tests. Use of a hand-held flashlight for ice detection is not acceptable. As described in § 23.1419(d), “The Airplane Flight Manual or other approved manual material must describe the means of determining ice formation and must contain information for the safe operation of the airplane in icing conditions.”
b. Dry Air Tests with Simulated Ice Shapes.
(1) Why Do Simulated Ice Shape Flight Testing? The installation of simulated ice shapes allows airplane performance and handling characteristics to be evaluated in stable dry air conditions with the critical ice shape being held constant (no change of ice accretion due to erosion, shedding, and so forth, that can occur with natural ice shapes). Dry air flight tests with simulated ice shapes installed also result in a considerable reduction in the amount of flight testing that would otherwise be required to accumulate the test ice shapes, and then evaluate their effects on airplane performance and handling characteristics in stable air.
(2) Flight Test Safety. Dry air tests with simulated ice shapes can be hazardous if not approached safely; therefore, the dry air flight test evaluation should be performed using a buildup technique, considering increases in spanwise coverage and dimensions of simulated ice shapes prior to full span ice shape tests.
(3) Simulated Ice Shapes.
(a) Critica l Ice Accretions. Consideration should be given to the type of ice protection systems (for example: mechanical, fluid, thermal, or hybrid), and the most adverse ice conditions (shape or shapes, texture, location, and thickness) for the relevant aerodynamic characteristics for the following, as appropriate: delayed system turn on, intercycle ice, failure conditions, runback ice, and residual ice. Consideration should also be given to unprotected areas. See paragraph 12c for more information. The validity of the ice shape predictions from analytical computations simulated icing flight tests or icing tunnel tests should be confirmed by flight tests in natural icing. These predictive methods should be conservative and should address the conditions associated with the icing envelope of part 25, Appendix C, that are critical to the airplane's performance and handling qualities in critical phases of the airplane's operational envelope, including climb, cruise, descent, holding pattern, approach, and landing. Ice shapes critical for performance may not be necessarily critical for handling qualities.
(b) Ice Detection Systems. For aircraft that have an ice detection system, consideration must be given to delays in ice detection and annunciation. These delays may include slow ice detector response at temperatures near freezing (low freezing fraction as discussed in AC 20-73) and the number of probe heat cycles utilized for annunciation or automatic ice protection activation.
(4) Flight Test Objectives.
(a) Performance. The effect of the ice shapes on stall speeds and airplane climb performance should be determined. Stall warning margins and maneuvering capability should also be evaluated. Operating speeds, stall warning speeds, and AFM performance information should be adjusted, if necessary, to provide acceptable performance capability and stall warning margins. The computation of the effects of ice on AFM performance should include reductions in engine power or thrust resulting from the applicable operating mode of the ice protection system.
(b) Handling Qualities. Handling characteristics are expected to degrade in icing conditions and should be investigated to determine that the “airplane is capable of operating safely.” For certification basis before amendment 23-43, subpart B requirements are used as guidelines. For certification basis at amendment 23-43 and higher, several subpart B requirements also apply in icing conditions. This is addressed in paragraph 12a. The results of these tests may be used in preparing specific AFM operating procedures and limitations for flight in icing conditions.
(c) Air Data Calibrations. If ice accretion is predicted to alter the position error of the production air data system (e.g. radome ice accretion), the position error would need to be determined using air data calibration flight tests (i.e. tower fly-by, trailing cone, speed course) with the critical, simulated ice shapes determined by analysis.
c. Flight Tests in Icing Conditions. Flight tests in measured natural icing and the use of simulated icing tools such as airborne icing tankers and icing wind tunnels are normally 25
employed to demonstrate that the ice protection system performs under flight conditions as the analysis or other tests indicate. They are also used to confirm the analyses used in developing the various components (for example, ice detectors) and ice shapes and, in the case of natural icing tests, to confirm the conclusions reached in flight tests conducted with simulated ice shapes. Testing should be accomplished at various points in the icing envelope of part 25, Appendix C, to verify the airplane's ability to safely operate throughout that icing envelope.
(1) Instrumentation. Sufficient instrumentation should be planned to allow documentation of important airplane, system and component parameters, and icing conditions encountered. The following parameters should be considered:
(a) Altitude, airspeed, and engine power.
(b) Temperatures. Static air temperature, engine component temperatures (for example, oil, heat exchanger fluids, cylinder head), electrical generation equipment temperatures, surface temperatures, interlaminate temperatures, and any other key temperatures that could be affected by ice protection equipment, by ice accumulation or other key temperatures that are necessary for validation of analyses
(c) Liquid water content can be measured using a hot-wire based instrument, calibrated drum, or other equivalent and acceptable means.
(d) Median volumetric droplet diameter can be approximately determined by using a drop snatcher to expose a gelatin oil or soot slide and then measuring the resultant impact craters, or by use of more sophisticated equipment such as a laser based droplet measuring and recording instrument.
(e) Cameras and dimensional reference aids to assist in determining ice accretion thickness and ice accretion coverage.
(2) Artificia l Icing.
(a) Why Do Artificial Icing Tests? Testing in artificial icing environments such as icing tunnels or behind airborne icing tankers represents one way to predict the ice protection capabilities of individual elements of the ice protection equipment. Due to the usually small dimensions of the artificial icing environment, testing is usually limited to sections of lifting surfaces, to components having small exposed surfaces such as heated pitot tubes, antennas, air inlets including engine induction air inlets, empennage, and other surfaces having small leading edge radii and windshields. Small components are more sensitive to the higher accumulation rates associated with high liquid water content and large droplet size. These conditions are easily simulated and not frequently encountered in natural icing flight tests.
(b) Airborne Icing Tankers. An artificial icing exposure may be obtained by the use of onboard spray nozzles forward of the component under examination or by flying the test 26
airplane in the cloud generated by an airborne icing tanker. Recommended procedures for airborne icing tanker testing, including instrumentation requirements, are in SAE ARP 5904, “Airborne Icing Tankers.”
(c) Icing Tunnels. Icing tunnel tests have been accepted for definition of preactivation, intercycle, residual, and runback ice on protected surfaces with the following considerations:
1. Scaling. A full-scale test article is preferable due to uncertainties in ice accretion scaling. To date the FAA has not accepted data on scaled models because of the uncertainties involved in the scaling laws.
2. Conformity. The test article must be conformed. Although parts of the ice protection system may be simulated, critical system parameters must be conformed. An example would be deicing boot steady state pressure, and pressure rise time and decay time.
3. Tolerances. Ice protection system tolerances on the production airplane, such as boot operating pressure, must be accounted for.
4. Operational Consideration. Proposed ice protection system operation (activation procedures, ice detection system delay, and deicing boot cycle times) must be accounted for in the test matrix.
5. Spray Times. If the facility cannot produce the required LWC, spray times can be adjusted to provide the equivalent water catch for part 25, Appendix C cloud lengths.
If large ice shapes are expected, test ambient temperature may have to be adjusted to provide an equivalent freezing fraction. Temperatures can change the ice adhesion/shed characteristics and this should be taken into account when adjusting test parameters. The test matrix should include longer times in continuous maximum conditions to evaluate the stability and cyclic nature of intercycle and residual ice. Certain unique design features, such as stall strips mounted on deicing boots, may not readily shed ice and spray times up to 45 minutes need to be evaluated.
6. Test Section. An outboard wing section is usually tested since it is typically more critical for aerodynamic degradations due to the reduced scale relative to the wing root (on wings incorporating significant taper ratios). It will also have higher water collection efficiency and may operate at a lower angle of attack, thereby promoting greater aft impingement of droplets on the suction surface. For thermal systems, the outboard sections also represent the extremities of the bleed air system where temperature and pressure losses are the greatest, which can be critical for runback accretions. The distribution of icing cloud parameters along the test span should be taken into account.
(3) Natural Icing.
(a) Why Do Flight Tests In Natural Icing Conditions? Section 23.1419(b) requires flight test in measured natural icing conditions. Flight tests in natural icing conditions are necessary to demonstrate the acceptability of the airplane and ice protection system for flight in icing conditions. AC 20-73 provides additional information that would be useful when establishing a natural icing flight test program.
(b) What Icing Conditions Should Be Tested?
1. Continuous maximum Icing Conditions. At least one exposure to icing conditions within the part 25, Appendix C, continuous maximum envelope should be obtained. The exposure should be sufficiently stabilized to obtain valid data. It is often difficult to obtain temperature stabilization in brief exposures. Additional exposures may be required to allow extrapolation to the envelope critical conditions by analysis. Test data obtained during these exposures may be used to validate the analytical methods used and the results of any preceding simulated icing tests.
2. Intermittent Maximum Icing Conditions. Past experience has shown that flight testing in natural intermittent maximum icing conditions may be hazardous due to accompanying severe turbulence and possible hail encounters that may extensively damage the test airplane. When design analyses show that the critical ice protection design points (that is, heat loads, critical shapes, accumulation, and accumulation rates, and so forth) are adequate under these conditions, and sufficient ground or flight test data exists to verify the analysis, then hazardous flight testing should be avoided.
(c) Documentation of Ice Accretions. During natural icing flight tests, ice accumulation on unprotected and protected areas should be observed and documented.
Remotely located cameras either on the test airplane or on a chase airplane has been used to document ice accumulations on areas that cannot be seen from the test airplane's flight deck or cabin. Visual devices such as rods and/or paint stripes may be used to aid in visual dimensional analysis of ice accretions. Care should be taken since some measuring devices may accrete ice and alter analysis of accretions on a surface of importance. The edges of paint stripes can be efficient ice collectors if not smoothed and must be accounted for. The location of all external instrumentation installed for icing flight tests, including cameras and visual devices, should be analyzed to verify that ice-shedding hazards are not introduced.
(d) How Much Ice Should Be Allowed to Accrete?
1. Normal Ice Protection System Operation. Sufficient data should be taken to allow correlation with dry air tests using simulated ice shapes. This should be accomplished with a target accretion thickness equivalent to the 45-minute dry air ice shapes on an unprotected part of the wing. Handling qualities and performance should be subjectively reviewed and determined to be in general correlation with those found in dry air testing. Refer to paragraph 12.a. for performance, stability, control and maneuverability requirements.
2. Delayed Ice Protection System Activation. In addition, flying qualities and performance should be qualitatively evaluated with the ice accumulations existing just prior to operation of deice (as opposed to anti-ice) components. The ice protection systems are to be activated by the flight crew in accordance with approved AFM procedures when icing conditions exist; however, for anti-ice components, tests should be conducted that simulate inadvertent icing encounters in which the pilot may not recognize that the airplane is about to enter an icing condition and the anti-ice component may not be activated until actual ice build-up is noticed.
How Long is the Delayed Activation? A delayed ice accumulation event of 30 seconds to two minutes has been used in these tests to simulate the flight crew's failure to recognize an icing condition. For engine ice protection systems, which for aft fuselage mounted engines can include the inboard wing ice protection system, a delay of two minutes is utilized to validate the ice shedding analyses and § 33.77 ice slab test results. For the delayed ice accumulation time event, consideration should be given to the icing conditions, the icing recognition means available, recommended crew procedures, and ice protection system performance of the particular aircraft. The tests to be accomplished are summarized in Table 4 of paragraph 12c of this AC.
(e) What Should Be Evaluated During Natural Icing Tests? All systems and components of the basic airplane should continue to function as intended when operating in an icing environment. Some considerations are:
1. Engine and equipment operation such as generator cooling under maximum load should be monitored during icing tests and be found acceptable for this operation.
2. Engine alternate induction air sources should remain functional in an icing environment.
3. Fuel system venting should not be affected by ice accumulation.
4. Retractable landing gear should be available for landing following an icing encounter. Gear retraction should not result in an unsafe indication because of ice accretion.
5. Ice shedding from components including antennas should cause no more than cosmetic damage to other parts of the airplane, including aft-mounted engines and propellers.
6. Stall Warning and Maneuver Margin. With ice accretions on the airplane, acceptable stall warning (aerodynamic or artificial) and stall protection, if a stall protection system is installed, should be provided to validate the results of the dry air ice shape testing. The stall warning should meet the requirements of § 23.307(a), (b), and (c). The type of stall warning in icing conditions should be the same as in no icing conditions. Biasing of the 29
stall warning and stall protection system, if installed, may be required to achieve acceptable margins to stall. The maneuver margin requirements § 23.207(d) should be demonstrated in icing conditions.
NOTE 1
This test and any handling qualities tests in natural icing should be accomplished in daytime visual meteorological conditions for safety.
7. Ice detection cues or ice detection system operation that the pilot relies on for timely operation of ice protection equipment should be evaluated in all anticipated flight attitudes.
8. Ice inspection lights should be evaluated in natural icing night conditions to verify that they illuminate ice build-up areas, are adequate under the conditions encountered, and do not introduce objectionable glare.
9. Flight Control Systems. Primary and secondary flight control surfaces should remain operational after exposure to icing conditions. Evaluations should confirm that aerodynamic balance surfaces are not subject to icing throughout the airplane's operating envelope (weight, Center Of Gravity (CG), and speed), or that any ice accumulation on these surfaces does not interfere with or limit actuation of the control for these surfaces including retraction of flaps for a safe go around from the landing configuration.
10. Air Data Systems. Ice accretions forward of pitot probes and static sources, such as accretions on radomes or other probes, should be evaluated to determine the effect, if any, on the position error of the aircraft’s production air data system.
11. Autopilot. All autopilot modes should be evaluated in natural icing conditions to validate the dry air ice shape test results. All autopilot modes should function properly in icing conditions. Airframe leading edge ice accretions could affect control power and control hinge moments resulting in incorrect autopilot gains. These evaluations should also show that autopilot actuators function properly and do not freeze up. The autopilot should be engaged for an extended period of time in natural icing conditions to check for unusual trimming and potential for ice to accrete in control surface gaps “control surface ice bridging.”
12. Pilot Workload. The workload in icing conditions should be evaluated when showing compliance to § 23.1523. Ice detection, ice protection system operation and monitoring, and autopilot operation and monitoring (including periodic disconnects), as a minimum should be evaluated.
12. PERFORMANCE AND HANDLING QUALITIES. Airplane performance and handling qualities are degraded by ice accumulations in various ways depending upon type, shape, size, and 30
location of these accumulations. If numerous unprotected areas exist, the weight and center of gravity effects of the ice formations should also be evaluated.
a. Flight Tests
(1) Section 23.1419 at Amendment 23-43 or Later. In accordance with § 23.1419(a), "capable of operating safely" means that airplane performance, controllability, maneuverability, and stability may be degraded from the non-iced airplane but must not be less than the requirements in part 23, subpart B. Guidance for each subpart B regulation, as related to icing, is in Appendix G. Unless noted otherwise, the guidance is applicable to all airplane categories for which compliance to § 23.1419 is being shown.
(a) Configurations and Flight Conditions. The handling qualities test matrix for ice shapes can be reduced from the basic (no ice) matrix, with concurrence from the administrator, to configurations and flight conditions that were deemed critical based on the no ice testing (basic aircraft certification). It is not required to test flight conditions at altitudes above the part 25, Appendix C icing envelopes.
(b) Harmoniz ation. The FAA and the European Aviation Safety Agency (EASA) are harmonizing the performance and handling qualities of part 25. This harmonization project will standardize the performance and handling qualities requirements, and provide additional guidance material for certification of part 25/large aeroplanes to safely operate in the icing conditions of part 25/CS-25, Appendix C. Much of this performance and handling qualities guidance has been adopted for part 23 airplanes and is presented in Appendix G. There have been some modifications for part 23 applications. For example performance criteria had to reflect different categories of airplanes (commuter category, normal category below 6,000 lb. maximum weight, and normal category above 6,000 lb. maximum weight). Also, stall speed tolerance criteria in some cases were modified to reflect lower stall speeds of part 23 airplanes compared to transport airplanes.
(c) Stall Speed. Section 23.1419, amendment 23-43, requires “…airplane performance…must not be less than that required in part 23, subpart B.” The stall speed requirements of § 23.49 are included in subpart B performance. For single engine aircraft that do not meet the emergency landing requirements of § 23.562(d), the stall speed at maximum weight must not exceed 61 knots. Recent flight testing of deicing boot-equipped aircraft with simulated intercycle/residual ice has shown stall lift coefficient losses of 17 percent to 23 percent with flaps extended. These lift losses were experienced on an airplane equipped with a stick pusher and on an airplane whose stall was defined by aerodynamic wing stall. This can represent a significant performance penalty for new aircraft if they had to be designed to meet the 61-knot stall speed requirement with ice on protected surfaces. Recently certificated single engine part 23 airplanes would most likely not meet this requirement since their no-ice stall speed in landing configuration is at or near 61 knots. Calculations on recently certificated single engine airplanes show that useful load in icing would have to be reduced by 40 percent in order to meet the 61-knot stall speed requirement with no major redesign.
In the notice of proposed rulemaking published in the “Federal Register” on October 3, 1990 (55 FR 40598), for the proposed rule that was to become amendment 23-43, the FAA stated the background for imposing subpart B requirements on part 23 airplanes versus part 25 transport airplanes: “The justification given was that normal and transport category airplanes must operate in about the same icing environment, but the normal category airplane is more likely to remain in icing conditions for longer periods of time because it may not have the performance capability to exit the icing environment as readily as transport category airplanes.”
Normal category airplane airfoils, being smaller than those of transport airplanes, are much more efficient collectors of ice, and their percentage drag increase in icing conditions are larger than transport airplanes. The requirement to meet subpart B performance was added to guarantee there would be a given level of excess power that could be used to exit icing conditions. An increase in stall speed in icing would not prevent an airplane from meeting the subpart B performance requirements if it was accounted for in analyses and testing.
For single-engine airplanes that do not meet the 61-knot stall speed requirement with critical ice accretions, the applicant should consider the following compensating features to propose an exemption to the stall speed requirement of § 23.1419(a), amendment 23-43. The exemption with the following compensating features would not adversely affect safety since it is safer to make a forced landing at higher speed than it is to inadvertently stall the airplane. There have been many fatal accidents in icing conditions attributed to the latter.
1. The airplane with no ice accretions meets the 61-knot stall speed requirement of § 23.49(c);
2. The airplane with critical ice accretions as defined in paragraph 12b of this AC complies with stall warning requirements of § 23.207.
(aa) For aircraft with artificial stall warning systems, paragraph 12a(1)2, may require a bias in the stall warning schedules to maintain adequate stall warning margins.
(bb) For aircraft without artificial stall warning systems, 12a(1)2, may require one to be installed to meet minimum stall warning margin requirements. Meeting § 23.207(d) may require an increase in operational speeds in icing to preclude nuisance stall warnings.
3. The AFM performance data in icing conditions reflects the higher stall and operating speeds.
4. Most importantly, the airplane with critical ice accretions has acceptable stall characteristics and is safely controllable with normal piloting skill as required by §§ 23.201 and 23.203.
5. The tire requirements of § 23.733 and brake requirements of § 23.735 are met with the higher stall and operating speeds.
6. The ground handling requirements of §§ 23.231, 23.233 and 23.235 and nose/tail wheel steering system of § 23.745, if applicable, are met with the higher landing speeds.
7. All other airplane system or testing requirements that could be affected by higher operating speeds, such as autopilot and flight director gains are evaluated.
8. Each seat/restraint system would have to include a safety belt and shoulder harness with a metal to metal latching device (this would address STCs on older airplanes that do not include § 23.785 in their certification basis).
9. The airplane certification basis would have to include § 23.1091 at amendment 23-51 and § 23.1093 at amendment 23-51 to provide the latest regulations for engine operation in icing conditions.
10. The airplane certification basis would have to include § 23.995 at amendment 23-29. This regulation was promulgated as a result of a National Transportation Safety Board (NTSB) recommendation and a 1983 study, which indicated at least half of off field forced landings were a result of fuel mismanagement.
The above approach represents only the minimum consideration, other issues may have to be considered depending on the aircraft design. In the petition for exemption, the applicant needs to state why it would be in the public interest and include the weight penalty in icing conditions as a result of complying with the 61-knot stall speed regulation.
(2) Section 23.1419 at Amendment 23-14. The definition of “capable of operating safely” is not defined in the regulation. The tests and pass/fail criteria of paragraph 12a(1) should be used as a guide to develop a test program that demonstrates the airplane is capable of operating safely in the part 25, Appendix C, icing envelope. The regulations italicized in Appendix G are not typically addressed in showing compliance to § 23.1419 at amendment 23-14.
b. Ice Accretions.
(1) Airframe Ice Accretions.
(a) Definition of Ice Accretions. The most critical ice accretions in terms of handling characteristics and/or performance for each flight phase should be determined. The parameters to be considered are the flight conditions (e.g., airplane configuration, airspeed, angle of attack. altitude) and the icing conditions of part 25, Appendix C (temperature, liquid water content, mean effective drop diameter). Table 3 summarizes the ice accretions for each flight phase for normal ice protection system operation.
TABLE 3. ICE ACCRETION DEFINITIONS
Ice Accretion Normal, Utility and Acrobatic Categories
Commuter Category Takeoff None if the AFM prohibits takeoff with ice, snow and frost on the wing and control surfaces. Otherwise, “polished” frost, as permitted by the parts 91 and 135 operating rules should be defined by the applicant and simulated for flight test evaluation if not prohibited for takeoff in the AFM.
Ice accretion occurring between liftoff and 400 feet above the takeoff surface, assuming accretion starts at liftoff in the “takeoff maximum icing” conditions, on:
• unprotected surfaces; and
• the protected surfaces appropriate to normal IPS operation; or
• the protected surfaces if IPS operation is prohibited for takeoff. (It should be assumed no flight crew action to activate the ice protection will occur until at least 400 feet above the ground level, or higher if specified in the AFM.)
“Takeoff maximum icing” conditions defined as:
• cloud liquid water content of
0.35 g/m3;
• cloud droplets Mean Effective Diameter (MED) of 20 microns; and
• ambient air temperature at ground level of minus nine degrees Centigrade (C)
Also includes simulated “polished” frost, as permitted by the parts 91 and 135 operating rules, as defined by the applicant, if not prohibited for takeoff in the AFM.